Swinging on Trains

Earlier this week, some pranksters wanted to bring some smiles to the San Francisco public. They installed three red swings on the BART Public Transit System. And then they left them there for the public to enjoy. Look at how much joy a swing can bring…

I was under the assumption that “swinging on trains” was
referring to a sexual encounter of a “committed” person with
another person; and that this activity took place in a train!
Also I noticed that only one person was using the swing at any time!